I have a AC/DC converter mounted , running directly from the battery. This converter is then used to plug in a laptop. from the laptop, i have an aux line going into the aux-in line.

when the AC/DC converter is on, there is a low freq noise on the line. if its off, no noise..


we tried
--------
puttin a cap. on the line to the laptop.
tying the PS's ground to the CAR's ground

neither worked

if headphones are hooked up to the laptop, no low freq noise.

first of all, what is causeing this? If i knew why this was, i could better find a way to solve it.

secondly, anyone know HOW to fix this?


Thank you SO much if you can help me.

 

A cap won't do it if you have stong power supply. You need some inductors too. You want the LC filter to have a 3db point that significantly lower than the hum you hear. A good stereo shop should be able to help you out.
One of the other things to look at is the various audio levels. Make the output level of your computer higher, and the gain at the head lower. In most cases, this can help as well. You also have to look for ground loops (the electrical path acting like an antenna) routing the wires next to sheet metal should minimize this effect. Good luck!

Matt

 

would grounding the audio line to the MINI's ground fix the ground loop problem?

 

What's happening is that hum from the power supply (could be the 12 to 120 or the power supply for the computer) is coming through to the audio out of you laptop. See if you run it on battery if it goes away....
Usually this coupling is worse at very low output volumes. You can check for the AC ripple with an oscilloscope, a DMM is usually not good enough to get good data. But you can look at the AC voltage coming out the audio with no track playing to see if your changes are making a difference.
If you are above your head in the electronics here, find a good audio shop to help out. It will be faster, and probably cost less in the long run....

Matt

 

yea, the sound does not show up using headphones. Why whould it show up when running to the cars stereo, but not headphones/laptop speakers?

btw, thanks for the help thus far

 

Would adding an isolation transformer/ground loop isolator help at all?

I'm just thinking that the audio ground on the HU is the same as the HU's power ground with is traveling with some noise from the battery over the audio cable.

Just a thought.

 

So i just fixed it. I grounded the audio line to the car and it fixed the issue.

My discription was a bit off. The buzzing occured before the aux line was even plugged into the laptop, meaning it was acting like an antenea. Grounding the line to the car works...

Thanks all for the help